nebris88 - He's a mindcracker, and is mentioned a lot by other users, but not many people watch his regularly. He's very productive in FTB, already having the white leggings (quantum?). He's a good builder, in both FTB and normal MC.
Youtube: http://www.youtube.com/nebris88

monkeyfarm - The Mob Trap Builder. Most have heard about him, but his LP world series is still not getting a lot. He's a new mindcracker, so he's not gotten famous there.
Youtube: http://www.youtube.com/monkeyfarm

There's also some more good ones if you poke around youtube for a few hours.